thanks, I know about inception, but I don't want to use this, because I want to add this to my script (n9 qtweak) and will tell to all users that need to install inception and opensh..
Any another way ?

none that i know of. AFAIK, pr1.2 makes it impossible to replace system files due to aegis hence some sort of hack is the way forward. Hoping for someone to find a workaround for this. Or can your script add the installation of inception and opensh, change the UA and then uninstall the two.

Yes grob is closed but at the other thread one user managed to change the hex values to show the UA of Android 4.0.1.

For pr1.2, do the following:
make a copy of the original grob to MyDocs.

run opensh in terminal after following the steps in inception thread.
replace the original grob with the modified grob.
after a reboot u need to copy back the original grob before replacing it again with the modified grob.

Can someone write a startup script to do this? Wish I was that good in Linux